In an experiment, uniform grinding of a sample of an animal or plant tissue and extraction of the components of the tissue to analyze the components has been widespread. Conventionally, a mortar and a pestle have been used to grind a sample, but the conventional mortars and pestles are not suitable for efficiently handling a very small amount of a sample or various samples because the conventional mortars are large. Units for efficiently grinding a small amount of a sample and various samples include a grinding unit that places a grinder of a particular shape into a vessel and moving the vessel in the figure eight pattern to grind the sample in the vessel (see Patent Literature 1: Japanese Patent No. 3834554). In the unit described in Patent Literature 1, the grinder of a particular shape is placed into the elongated vessel, together with a sample to be ground, and the vessel is moved in the figure eight pattern. As a result, the grinder repeatedly hits the bottom of the vessel while relatively rotating. Thus the vessel and the grinder act as a mortar and a pestle respectively to effectively grind the sample.
There is also a unit for grinding a sample by inserting the sample and a plunger into a tube with a filter at the bottom; rotating the plunger to crush the sample; pressing the plunger; and centrifuging the tube and the plunger to force the sample to pass through the filter to yield the fine particles (see Patent Literature 2: Japanese Patent No. 3853794). According to Patent Literature 2, the grinding process comprises pressing the sample using the plunger and thus can achieve a higher collection of the ground sample and a higher security than the process of only applying centrifugal force to force the sample to pass through the filter to yield the fine particles. And the unit according to Patent Literature 2 can simultaneously grind plural samples and thus can improve operating efficiency.
The unit described in Patent Literature 1, however, is required to move the vessel which contains a sample in the figure eight pattern to grind the sample. Thus it is necessary to prepare a special grinding tool which can provide such movement. This means that conventional tools cannot be used in the unit and that the installation is costly and time consuming. Additionally, the grinder is made of magnetic stainless steel such as SUS430, hard stainless steel such as SUS304, titanium, tungsten, glass, or the like. The grinder is required to be washed and/or the like for next use, which may cause contamination or reduce the maneuverability. Furthermore, because a sample is ground only when the grinder falls onto the vessel under its own weight, some samples are difficult to be sufficiently ground.
On the other hand, the grinding process described in Patent Literature 2 comprises rotating a pressing member which is provided with protrusions extending radially at the bottom thereof to crush a sample between the pressing member and the filter, and then passing the ground sample through the filter by centrifugation. The process is suitable for grinding relatively flexible tissues such as brain and liver tissues. Additionally, the unit is made of plastic and thus is disposable to prevent contamination. A fibrous tissue such as a muscle tissue, however, cannot be sufficiently ground only with the protrusions formed on the bottom of the pressing member as described above. Even when the ground tissue is subsequently centrifuged, such tissue is difficult to be passed through the filter to yield the fine particles, and thus the collection of the tissue may be reduced.